The present invention relates to an automobile speed control system for automatically controlling an automobile to run at a stored speed, and more particularly to an automobile speed control system capable of storing a plurality of different speeds and controlling an automobile to cruise at a selected one of the stored speeds.
Prior automobile speed controls detect a current automobile speed as a number of pulses and produces an analog voltage commensurate with the number of pulses as a signal indicative of the current automobile speed. When the automobile reaches a desired speed, the driver depresses a speed set switch to set or store the speed signal at that time into a speed memory. The speed control includes a comparator for comparing a signal representative of a current automobile speed with the stored speed signal which serves as a reference voltage. The speed of the automobile can be maintained at the desired value by adjusting the opening of a throttle valve in the engine on the automobile in order that any difference between the compared signals will fall to zero.
One known example of such an automobile speed control is disclosed in U.S. Pat. No. 4,196,787 issued on Apr. 8, 1980 to the same assignee.
The prior automobile speed control system is capable of storing only one selected speed value. When the driver wants to lower the automobile speed down to 40 Km/h while the automobile is running at the speed of 60 Km/h under automatic speed control, the driver is required to release the speed control to let the automobile slow down, and then depress the speed set switch when the speedometer reading reaches 40 Km/h to resume the speed control. However, such manual speed changing operation is considerably awkward while driving the automobile. Automobiles are legally required to observe speed limits such as 40 Km/h, 60 Km/h, and 80 Km/h imposed on various kinds of roads and highways. It is therefore normal practice for automobiles to run on roads and highways at their speed limits. When an automobile enters a different road having a different speed limit, the automobile has to change its speed. Upon setting and storing a new speed after the automobile has changed it speed, previous stored speed data is erased. If the automobile is to be restored to the previous speed, then the driver has to perform the awkward speed changing operation once again.